1. Field of the Invention
The present invention relates to the display of information items on display devices known as head-up, and more particularly to a crossed monitoring device for display units of this type, making it possible, especially for a pilot in an aircraft, to view, via his display unit, the information items presented on the display unit of the pilot seated beside him.
Aircraft cockpits are generally not equipped with display devices known as head-up, also called HUD (initials for Head-Up Display in English terminology), but are equipped with conventional CRT or flat screens installed in the instrument panels. These conventional screens generally have viewing angles sufficiently broad to permit a pilot seated in the left position to have visual access to all of the information items displayed on the screens at the right and vice versa.
Consequently, in a traditional cockpit, it is possible for a pilot to access the entirety of the information items presented on the different screens. In particular, it is basic on the primary piloting screen, known as PFD (initials for Primary Flight Display in English terminology), where the pilots often have a need to verify the validity of their primary flight parameters, such as attitude and speed. In fact, parameters originating from a first set of sensors are presented on the screens at the left and parameters originating from a second set of sensors are presented on the screens at the right. This segregation permits a pilot to monitor his own parameters in independent manner.
On a head-up display device, the problem is different, inasmuch as the information items projected onto the HUD screen can be observed only in a limited volume of space known as the eye box (eyebox in English terminology). This eyebox, which has limited dimensions, is centered around the eye of the pilot. In certain aircraft, such as military airplanes, it permits the use of night-vision goggles.
FIG. 1 shows an aircraft cockpit 100 comprising eight head-down screens, referenced 105-1 to 105-8, and two head-up screens, referenced 110-1 and 110-2. Thus the pilot on the left is able to view information items displayed on the screens in front of him, or in other words here on screens 105-1 to 105-4 and 110-1, as well as on the head-down screens situated in front of the pilot situated on the right, or in other words here on screens 105-5 to 105-8. Similarly, the pilot on the right is able to view information items displayed on screens 105-5 to 105-8 and 110-2, as well as on head-down screens 105-1 to 105-4.
FIG. 2 illustrates the principle of a head-up screen comprising a projector 200 and an at least partly transparent screen 205, on which there are projected the information items to be displayed. Reference 210 schematizes an eyebox in which the eyes of a user 215 must be situated if the user is to be able to view the information items projected by projector 200 onto screen 205.
Considering the state of the parameters available on the communication buses to which the head-up display system is connected as basis, and taking the manual selections of the pilot into account, a computer known as HUDC (initials for Head-Up Display Computer in English terminology) generates a digital video image which is then transmitted to the projector, known as HPU (initials for Head-Up Projection Unit in English terminology), for display. The projected digital video image is usually generated on the basis of data originating from sensors and of graphical symbols, forming a symbology represented by the digital video image.
Viewed from the side, as illustrated in FIG. 2, an eyebox has a length of approximately 10 cm. Thus it is not possible for a pilot to have direct access to the information items presented in the HUD of his neighbor.
This problem is crucial for aircraft in which the HUDs are being used as the primary piloting instrument, or in other words for aircraft in which the pilots have the option of not displaying the PFD on the head-down screens.
As described in the foregoing, each HUD constructs its image on the basis of a selection of data. In practice, certain information items pertaining to a first set of sensors can be selected to be displayed on a first HUD. Similarly, certain information items pertaining to a second set of sensors can be selected to be displayed on a second HUD. Consequently, each HUD has its own source-selection function, which depends on the side on which the HUD is installed.
2. Description of the Related Art
According to a known solution, shown in FIG. 3, a crossed communication bus is established between the different HUDs, to permit them to exchange selected information items pertaining to the different sets of sensors.
Upon a command of the pilot, via a button dedicated to crossed monitoring and accessible on a control panel, the HUD uses the selected information items originating from sensors associated with another HUD to generate an image based on the same information items as those displayed on another HUD.
FIG. 3 illustrates this solution when two HUDs are used. The first HUD, referenced 300-1, comprises a computer 305-1, a projector 310-1 and a projection screen 315-1.
Via communication bus 320-1, computer 305-1 receives information items from a sensor group divided into two corresponding subgroups, such as a right subgroup and a left subgroup. Some of those information items are selected by the pilot so as to be displayed. The selected information items are used to form an image, which is transmitted to projector 310-1 to be projected onto screen 315-1.
Similarly, the second HUD, referenced 300-2, comprises a computer 305-2, a projector 310-2 and a projection screen 315-2. The selected information items, originating from communication bus 320-2, are used to form an image, transmitted to projector 310-2 and projected onto screen 315-2.
A communication bus 325 connects computers 305-1 and 305-2 in such a way that the data selected in computer 305-1 are transmitted to computer 305-2 and, reciprocally, the data selected in computer 305-2 are transmitted to computer 305-1.
Computers 305-1 and 305-2 additionally comprise commands 330-1 and 330-2 respectively, which make it possible to determine which selected information items must be displayed. According to a common mode of operation, the selected information items originating from the set of sensors associated with the HUD under consideration are displayed, while in a crossed mode of monitoring the selected information items originating from the set of sensors associated with the other HUD are displayed.
According to this method, it is therefore necessary to manage the selection of data sources, to manage a communication bus between the computers being used and to acquire the data originating from several sets of sensors.
Although this solution permits crossed monitoring of information items displayed in the HUDs, it has several drawbacks, especially in terms of segregation of data and in terms of reliability.